1. Field of the Invention
The present invention relates generally to body implantable leads, and more specifically relates to leads capable of interfacing with both the ventricle and atrium of the heart.
2. Description of the Prior Art
With the advent of atrial-ventricular (A-V) pacing, the necessity to electrically interface with both atrial and ventricular tissue has become a necessity. This may be accomplished through the use of two separate leads. One lead is placed in the atrium in the normal fashion whereas the second lead is placed within the ventricle in the normal fashion. Typical implant techniques use either a single vein for implantation of both leads or a separate vein for each of the leads to be introduced. A second approach and one thought to be simpler in implementation is the use of a single-pass lead.
U.S. Pat. No. 4,057,067 issued to Lajos is an example of a single-pass lead. The lead taught by Lajos has a single lead body which, at a point relatively near the distal end, results in a ventricular branch and an atrial branch. The ventricular and atrial branches are located at a fixed distance from one another. Therefore, the possible implant position of the ventricular electrode relative to the implant position of the atrial electrode is fixed and can not vary with variations in the size of the heart to be stimulated. The primary method for overcoming this problem is the use of single-pass leads employing the slider concept. The slider concept allows the length of the ventricular and atrial branches to be adjusted relative to one another. The slider concept is thus more easily implanted and makes provision for variations in heart size.
The major disadvantage of using the slider concept in a single-pass lead involves the difficulties associated with sealing the position at which the ventricular and atrial branches emerge from the common sheath. A second problem is experienced at the proximal end in connecting both branches to a common pulse generator. The assignee of the present invention has a number of patent applications on file which employ the slider conept in the single-pass A-V lead. These inventions tend to be directed toward a method of overcoming these difficulties associated with sealing the branchpoint and making proper connection to the common pulse generator.
The present invention does not employ the slider concept. Because the ventricular and atrial electrodes are at a fixed distance from one another, compensation must be made for variations in heart size. Leads which use something other than a straight line of transit between the electrode at the distal tip and the superior vena cava are also known. Dutcher, in U.S. Pat. No. 4,135,518 teaches a ventricular lead wherein the fixation technique involves use of some slack within the lead body. Dutcher uses a weighted distal tip in combination with a very flexible portion of the lead between the distal tip and some point proximal to that for encouraging enlodgement of the electrode in the right ventricular apex. It is interesting to note that Dutcher teaches the use of this slack within the lead to aid in fixation of the electrode and teaches only placement of this slack within the ventricle.
A second lead taught in U.S. Pat. No. 4,154,247 by O'Neill, uses a far more rigid amount of slack as a fixation means. O'Neill shows that a lead constructed in the manner in which he teaches can, through its rigidity, be forced to maintain contact with the tissue to be stimulated.